Physical capacity declines earlier than you think – here’s how you can stay strong

When does fitness level decline, and how can I stay fit as I age?

Physical capacity often changes much earlier than we realise. Many people are active earlier in life, then gradually drift away from exercise while work, stress, and family responsibilities take priority. Often there’s an assumption they’ll simply “get back to it later”. But the reality is physical capacity is not as stable as we might assume.

A 2025 study by Westerstahl and colleagues followed the same 427 people for 47 years, tracking their fitness from age 16 to 63. The researchers found aerobic fitness, muscular endurance, and power generally peaked between the late 20s and mid-30s. After that, physical capacity gradually declined - and the rate of decline accelerated with age.

By age 63, many measures of physical capacity had declined by roughly 30-48% from their peak levels. That’s important, but there was a silver lining too: People who became physically active later in adulthood still meaningfully improved their physical capacity. In other words, the trajectory was still modifiable later in life.

It’s an important reminder that waiting until something feels “wrong” may mean decline has already been building for years. Because while ageing is inevitable, loss of physical capacity is not completely fixed.

The earlier we build and maintain strength, fitness, and movement habits, the better - but it’s also never too late to improve your trajectory. 

At Kieser, we help people maintain the strength and physical capacity that supports long-term health, independence, and quality of life. Because it’s never too early - or too late - to start investing in your future health. Strength training is approached as more than just building muscle. It’s about improving the strength, confidence, and function that support long-term independence and healthy ageing.

Reference:

Westerstahl, M. et al. (2025). Rise and Fall of Physical Capacity in a General Population: A 47-Year Longitudinal Study. Journal of Cachexia, Sarcopenia and Muscle, 16(6), e70134.